
package com.csscis.ssm.core.feature.orm.dialect;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author QingHe
 * @since 2014年5月18日 下午1:33:01
 **/
public class MySql5PageHepler extends DialectHelper {

    /**
     * 得到查询总数的sql语句
     *
     * @param querySelect 传入的SQL语句
     * @return            查询总数的SQL语句
     */
    public static String getCountString(String querySelect) {

        querySelect = getLineSql(querySelect);
        int orderIndex = getLastOrderInsertPoint(querySelect);
        int formIndex = getAfterFormInsertPoint(querySelect);
        String select = querySelect.substring(0, formIndex);

        // 如果SELECT 中包含 DISTINCT 只能在外层包含COUNT
        if (select.toLowerCase().indexOf("select distinct") != -1
            || querySelect.toLowerCase().indexOf("group by") != -1) {
            return new StringBuffer(querySelect.length()).append("select count(1) count from (")
                .append(querySelect.substring(0, orderIndex)).append(" ) t").toString();
        } else {
            return new StringBuffer(querySelect.length()).append("select count(1) count ")
                .append(querySelect.substring(formIndex, orderIndex)).toString();
        }
    }

    /**
     * 得到最后一个Order By的插入点位置
     *
     * @return 返回最后一个Order By插入点的位置
     */
    private static int getLastOrderInsertPoint(String querySelect) {

        int orderIndex = querySelect.toLowerCase().lastIndexOf("order by");
        if (orderIndex == -1) {
            orderIndex = querySelect.length();
        }
        if (!isBracketCanPartnership(querySelect.substring(orderIndex, querySelect.length()))) {
            throw new RuntimeException("My SQL 分页必须要有Order by 语句!");
        }
        return orderIndex;
    }

    /**
     * 得到分页的SQL<br/>
     * <p/>
     * 主要是把传入的sql合并为一行并删除多余空白，再在后面添加 limit 'offset' , 'limit'
     *
     * @param querySelect 传入的SQL语句
     * @param offset      偏移量
     * @param limit       需要的当前页记录数
     * @return            分页SQL
     */
    public static String getLimitString(String querySelect, int offset, int limit) {

        querySelect = getLineSql(querySelect);

        String sql = querySelect + " limit " + offset + " ," + limit;

        return sql;

    }

    /**
     * 得到SQL第一个正确的FROM的的插入点
     */
    private static int getAfterFormInsertPoint(String querySelect) {

        String regex = "\\s+FROM\\s+";
        Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
        Matcher matcher = pattern.matcher(querySelect);
        while (matcher.find()) {
            int fromStartIndex = matcher.start(0);
            String text = querySelect.substring(0, fromStartIndex);
            if (isBracketCanPartnership(text)) {
                return fromStartIndex;
            }
        }
        return 0;
    }

    /**
     * 判断括号"()"是否匹配,并不会判断排列顺序是否正确
     *
     * @param text
     *            要判断的文本
     * @return 如果匹配返回TRUE,否则返回FALSE
     */
    private static boolean isBracketCanPartnership(String text) {

        if (text == null || (getIndexOfCount(text, '(') != getIndexOfCount(text, ')'))) {
            return false;
        }
        return true;
    }

}
